.\" Copyright (c) 2022 Klara Systems
.\"
.\" This software was developed by Mitchell Horne <mhorne@FreeBSD.org>
.\" under sponsorship from Juniper Networks and Klara Systems.
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.Dd June 29, 2022
.Dt MAC_DDB 4
.Os
.Sh NAME
.Nm mac_ddb
.Nd "Restricted kernel debugger interface policy"
.Sh SYNOPSIS
To compile the ddb policy
into your kernel, place the following lines in your kernel
configuration file:
.Bd -ragged -offset indent
.Cd "options MAC"
.Cd "options MAC_DDB"
.Ed
.Pp
Alternately, to load the ddb module at boot time, place the following line
in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "options MAC"
.Ed
.Pp
and in
.Xr loader.conf 5 :
.Bd -literal -offset indent
mac_ddb_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
policy module implements a MAC policy which restricts the set of commands that
can be used at the
.Xr ddb 4
command prompt.
The subset of permitted commands is limited to those which do not read or write
to arbitrary memory locations.
This is done to deter the possible extraction of system secrets while still
allowing enough debugger functionality to diagnose a kernel panic.
For example, the
.Ic trace
or
.Ic show registers
commands are allowed by this policy, but
.Ic show Cm buffer Ar addr
is not.
.Pp
All debugger commands that are declared with the
.Va DB_CMD_MEMSAFE
flag are allowed by
.Nm .
The policy provides validation functions to conditionally allow some additional
commands, based on the user provided arguments.
.Pp
When loaded, the
.Nm
policy also ensures that only the
.Xr ddb 4
debugger backend may be executed;
.Xr gdb 4
may not.
.Ss Label Format
No labels are defined for
.Nm .
.Sh SEE ALSO
.Xr ddb 4 ,
.Xr mac 4 ,
.Xr mac_biba 4 ,
.Xr mac_bsdextended 4 ,
.Xr mac_ifoff 4 ,
.Xr mac_lomac 4 ,
.Xr mac_mls 4 ,
.Xr mac_none 4 ,
.Xr mac_partition 4 ,
.Xr mac_portacl 4 ,
.Xr mac_seeotheruids 4 ,
.Xr mac_test 4 ,
.Xr mac 9
.Sh BUGS
While the MAC Framework design is intended to support the containment of
the root user, not all attack channels are currently protected by entry
point checks.
As such, MAC Framework policies should not be relied on, in isolation,
to protect against a malicious privileged user.
